1. Field of the Invention
The field of the invention is, in general terms, that of motor vehicle headlamps.
2. Description of the Related Art
In this field, various types of device are known, intended for illuminating the road or for signalling, among which there are essentially:
tail lights of low intensity and range;
long-range headlights, or high beam lighting devices, and supplementary lighting devices of the long-range type, whose area of vision on the road is around 200 meters and must be switched off when passing another vehicle in order not to dazzle its driver; these are beams without cutoff;
fog lights;
passing beam or low beam lighting devices, of high intensity and with a range on the road of around 70 meters;
improved headlamps, referred to as dual function, which combine the functions of low beams and high beam incorporating a removable shade;
signalling devices, for example of the turn indicator type etc. indicator type etc.
There exist two main families of optical module, which correspond to two distinct arrangements of the different elements, and which are able to act in the device according to the invention. Optical module means an optical system comprising at least one light source, for example a halogen lamp or a xenon lamp, disposed in a reflector, and which is preferably self-contained, that is to say which is able to be switched on or off separately from the other optical modules of the lighting device in which it is installed if the latter comprises several optical modules.
The two main families of optical modules are as follows:
The first family is that of so-called elliptical optical modules. In this type of optical module, a light concentration spot is generated by a light source disposed in a mirror, or reflector. Typically, the light source is disposed at the first focus of an ellipsoid-shaped mirror, the spot forming at the second focus, or image focus, of the mirror. The light concentration spot is then projected onto the road by a convergent lens, for example a lens of the plano-convex type.
The second family is that of so-called parabolic optical modules. In this type of optical module, a light beam is generated by a small light source disposed in a reflector, or mirror. The projection onto the road of the light rays reflected by a suitable reflector makes it possible to obtain directly a light beam complying with the various constraints imposed by standards. This family of optical module includes so-called free-surface, or complex-surface, headlamps, which make it possible to obtain directly a light beam having a desired cutoff line.
The present invention is more particularly adapted to lighting devices of the first family.
In the prior art, a lighting device of the generic elliptical type is typically of the same type as that depicted in FIG. 1. FIG. 1 depicts a view in section and from the side of a low beam lighting device 100 that comprises essentially a reflector 101, roughly ellipsoidal in shape, a light source 102 emitting a plurality of light rays 103 and disposed in the vicinity of the top of the reflector 101, and an exit surface 104, for example an outer lens made from plastics material, for a light beam 106. Before reaching the exit surface 104, the light rays 103 are caused to pass, either directly, or after reflection on the reflector 101, through a projection lens 105, characterized by an entry face 110 and an exit face 111. It projects the light beam 106, whose orientation and range depend in particular on the arrangement and optical characteristics of the projection lens 105, the shape of the reflector 101, the position of the light source 102 within the reflector 101 and the possible presence of a shade and the position thereof. Preferably, a central part of the light source 102 is disposed in the focal area of a first focus F1 of the reflector 101, and the object focus of the projection lens 105 is situated in the focal area of a second focus F2 of the reflector 101. Thus any light ray 103 emitted by the central part of the light source 102 passes through the second focus F2 of the reflector 101 and leaves the projection lens 105 horizontally.
In this example, a shade 108 is interposed between the reflector 101 and the projection lens 105. The shade 108 is disposed in a plane parallel to the projection lens 105, approximately level with the object focal plane of the projection lens 105, so that the image of the shade 108 is emitted to infinity. By virtue of the presence of such a shade 108, the light beam 106 that is effectively emitted by the lighting device 100 is not emitted above a cutoff line determined by the shape of a top part 109 of the shade 108.
Having a light source disposed, in the direction of its length, in line with the foci F1 and F2 of the reflector 101 gives a particularly elongated shape to the reflector 101. Moreover, the fact that it is necessary, for thermal reasons, to keep a certain distance between the projection lens 105 and the exit lens contributes to the elongate shape of the lighting device in question. Thus the general size of conventional elliptical lighting devices of the prior art is great in the direction of their length. They therefore require, in the vehicle in which they are intended to be placed, great depth. Such a spatial size thus does not make it possible to adapt to locations where the available space is reduced in depth; however, such considerations, in particular because of changes in the requirements of manufacturers, in particular in terms of style, are more and more frequent.
A problem is therefore posed for the design of certain lighting devices, the volumes that are reserved for them now having less conventional shapes than previously.